A. Field of Invention
This invention pertains to a microprocessor controlled infusion pump for delivering drugs to a patient, and more particularly to an infusion pump with a memory cartridge which defines one of a variety of configurations for the pump, said cartridges being replaceable to allow the pump to be used in multiple, different environments.
B. Description of the Prior Art
Infusion pumps are used in the field of medicine to administer drugs to patients over an extended time period particularly durations longer than can be managed easily by direct injection. As availability of drugs, therapeutic techniques, and technological capability have improved, the demand for sophistication in drug delivery has increased. In many instances, this added sophistication results in more complicated device operation. Achieving this sophistication in drug delivery capability, and maintaining ease of use has been a major challenge for infusion pump manufacturers.
One reason that devices have become complicated is the breadth of drug dosing methods used. For example, such different modes of operation as Patient Controlled Analgesia (PCA) and physician interactive dosing for operating room infusions must somehow be accommodated. Other current therapy modes in use include continuous infusion, bolus plus continuous infusion, clinician interactive dosing, PCA with continuous infusion, time/dose, and multiple automatic time/dose.
Continuous infusion is the most traditional method of drug delivery. FIG. 1 shows a graph of a constant drug flow vs. time. The infusion rate may be changed, if necessary, but whatever rate is selected will continue indefinitely. In this type of infusion, the user only selects the rate in ml/hr or drops/minute.
Time/dose therapy is shown in FIG. 2. This therapy is accomplished with a number of different devices for many different drugs. One device, a syringe infusion pump described in U.S. Pat. No. 4,544,369, has no rate input at all. The selection of syringe size and dose volume define the duration of infusion and, thus, the flow rate. Other devices have flow rate and dose volume as inputs. Still others require dose volume and duration of infusion as inputs. Intermittent medications such as antibiotics and H.sub.2 agonists are often administered using these devices.
FIG. 3 shows a multiple dose scheme. This method is similar to time/dose, but also includes a repeat time as a user defined parameter. The pump automatically starts each dose at predetermined time intervals.
FIG. 4 shows patient controlled analgesia (PCA) therapy. The clinician typically selects a dose size, and a minimum delay or lockout period. The patient may request a drug dose using a bedside request button connected to the pump. The pump administers a dose only if it has been requested during the minimum time period after the administration of a previous dose.
Often, a continuous infusion is superimposed over PCA therapy as shown in FIG. 5. The clinician must select a continuous infusion rate along with the dose size and minimum delay period. PCA therapy may also include additional clinician selectable features. These include a loading dose at the start of or during therapy and secondary prescription limits (e.g. hourly limit).
Interactive dosing is commonly done in the operating room (OR) or the intensive care unit (ICU). FIG. 6 shows a typical course of therapy. The clinician selects appropriate rates, boluses, and changes based on patient response or therapeutic goal. Aspects of interactive dosing are common to all infusion schemes because the actual dosing requirements change from patient to patient and from time to time. Nevertheless, certain circumstances require rapid interactive dosing not necessarily available or even desirable on all devices. An example of a device particularly well suited for this type of interactive dosing is made by C. R. Bard and is described in U.S. Pat. No. 4,943,279.
Of particular importance to the foregoing discussion is the wide variety of user selectable primary dosing inputs. The range of possible user inputs includes, but is not limited to, infusion rate, infusion duration, dose volume, lockout period, repeat period, bolus size, and bolus rate. Secondary inputs may include patient weight, patient sex, syringe size, container volume, security codes, drug units (e.g. milligrams), drug concentration, or even pharmacokinetic parameters.
In addition, not only are the clinician inputs numerous and variable, but the infusion pump's outputs are also extensive. History and status information unique to each therapy must be presented to the user in a clear manner.
The totality of inputs and outputs is termed the user interface. This user interface often has one most desirable features for a particular therapeutic modality.
Because of the large number of therapeutic modalities and the extensive number of possible required inputs and outputs, the challenge to manufacturers has been great. Users desire most a user interface with only a particular set of inputs and outputs pertinent to a particular therapy. On the other hand, great versatility is desired by both the manufacturers and the users. Users desire versatility so their pumps can perform many therapies. Manufacturers have the same desire because the economies of scale can be more easily realized.
The infusion industry has collectively responded to these needs in a number of ways. First, compromises in features are often accepted in the interest of having versatile, general or multi-purpose pumps. For example, users may sometimes select doses based on body weight and drug units, but often times this may not be current practice for some drugs. Therefore when necessary, users perform conversion calculations so that rates may be selected in ml/hr. These calculations are time consuming and are potential error sources. Another example is that continuous infusion modes may be used for time/dose infusions. The user must either time the infusion or rely on "end of container" alarms to appropriately terminate delivery.
An alternate to general purpose pumps has been devices designed specifically for only one drug or therapy. This has proven desirable for some widespread therapies. Users value the simple operation of these devices since they include only those features needed for a particular therapy. The disadvantage of these devices is their lack of versatility. They usually cannot perform widely differing therapies, nor can they accommodate therapy advance over time.